Field of the Invention
The present invention relates to a magnetic recording medium, essentially consisting of a polymeric substrate and at least one coherent, magnetic thin metal film which is present on the surface of the substrate and is deposited in the PVD process on the polymeric substrate moved longitudinally past an evaporation crucible, and a process for the production of the magnetic recording medium, in which a vapor jet obtained by evaporating a magnetic metal or a magnetic alloy is deposited in the form of a coherent, magnetic thin metal film on a longitudinally moving polymeric substrate,
The application of thin metal films to polymeric substrates is of interest particularly in the production of magnetic recording media. Compared with the conventional particulate magnetic media, coherent thin magnetic films permit recording with higher storage densities. This is due on the one hand to the small layer thickness of only from 20 to 1000 nm and the associated low demagnetization effect and on the other hand to the relatively large number of elementary magnets per unit volume and the resulting higher magnetization. Whereas in the case of the particulate recording media longitudinal recording by means of magnetic particles oriented along the tape playing direction is usual, oblique orientation of the elementary magnets in the coherent metal film, adapted to the field lines in front of the head, is desirable in the case of the thin magnetic films having a high storage density. By oblique deposition of the ferromagnetic material on the substrate, it is possible to achieve substantially improved recording properties, as described, inter alia, in U.S. Pat. No. 3,342,632 U.S. Pat. No. 4,323,629 with regard to the Co-Ni-O films or by R. Sugita et al., Digest Intermag 1990, Article FA-08, with regard to the Co-Cr films. The particular desired angular range, which decisively influences the properties of the applied magnetic layer, is obtained in the vapor deposition or sputtering of the magnetic material by correspondingly arranged evaporator sources or sputter cathodes and screens.
It is known that the thin metal film can be formed in the presence of oxygen in order to improve the adhesion of the metal film to the substrate and also to ensure sufficient mechanical stability, in particular of the surface layers of the metallic magnetic film (DE-A-32 41 775). However, it has been found that even small amounts of oxygen lead to a reduction in the residual induction and to an increase in the coercive force, which may be very undesirable.
It is an object of the present invention to provide a magnetic recording medium having a large residual induction component in the plane of the film and in particular high residual induction in the transverse direction, i.e. perpendicular to the playing direction of the film, the coercive force being &gt;10 kA/m, and a process which permits the production of such recording media having constant quality.